We will explore the effects upon human lymphocyte proliferation of monocytes and other cellular and humoral elements in cultures as well as regulatory effects of hormones and chemotherapeutic agents. Stimulation and control of DNA synthesis and cell division will be studied in cultures of lymphocytes obtained from normal donors, patients with immunological diseases and patients with lymphocytic malignancies. Accurate quantitation of the number of responding cells and of cell cycle kinetics will be carried out with lymphocytes exposed to nonspecific mitogens and antigens. The role of monocytes in lymphocyte-mediated "natural or "spontaneous" cytotoxicity against tumor cells will also be investigated.